Conventionally, in an enterprise or the like, data is typically stored in a storage apparatus known as a disk array subsystem in which a plurality of memory apparatuses such as SSD or Hard Disk Drives (HDDs) are installed.
In this type of storage apparatus, RAID (Redundant Array of Inexpensive Disks) groups are configured from one or more memory apparatuses of the same type and logical storage areas called ‘volumes’ are defined in the storage area provided by the memory apparatuses which a single RAID group comprises. Data from a host computer (referred to hereinafter as a host apparatus) is read/written from/to these volumes.
Note that SSDs are advantageous owing to their superior reliability and responsiveness in comparison to hard disk drives, and hence it is thought that SSDs will be adopted more and more as memory apparatuses in storage apparatuses. However, SSDs have the disadvantage that there are limitations on the number of times they can be rewritten due to the resulting degradation of the semiconductor storage elements, and that the cost per bit is high in comparison with that of hard disk drives.
Hence, as the volumes of data managed by enterprises and other organizations are increasing year by year, the effective usage of storage apparatuses has become an important issue. In order to solve this problem, data management technologies such as hierarchical storage management and Thin Provisioning and so on have conventionally been proposed.
For example, Japanese Patent Laid-Open Publication No. 2006-099748 discloses a hierarchical storage management technology with which volumes that are defined in a storage apparatus are classified into groups called ‘storage layers’ according to the characteristics of the memory apparatuses providing the storage area such as their reliability and response performance, and with which technology data is arranged in the optimum hierarchical storage volumes according to cost and the number of access inputs/outputs per unit time. Effective usage of memory apparatuses can be achieved using such hierarchical storage management technology.
Furthermore, Thin Provisioning technology is designed to improve the capacity utilization of storage apparatuses. In a normal non-Thin Provisioning volume, a storage area equivalent to the total capacity of the volume is reserved when the volume is created, and hence a corresponding storage area must be pre-prepared.
Meanwhile, in Thin Provisioning technology, a pool (referred to hereinafter as a ‘virtual pool’) is configured from a plurality of volumes and a ‘virtual volume’ (labeled as such hereinafter) is built on this virtual pool. This virtual volume is then provided to the host apparatus, and a physical storage area is only allocated, from the volume in the virtual pool, to unit areas (hereinafter referred to as ‘data blocks’) to which data in the virtual volume is written).
According to such Thin Provisioning technology, a storage area equivalent to the total capacity of the virtual volume need not be prepared even when creating a large-capacity virtual volume. It is sufficient to prepare a storage area only amounting to what is actually used by the host apparatus. The capacity utilization of the storage apparatus can therefore be improved.